Rotary drill bits of the type employed for drilling wells, blast holes and the like commonly employ two or three inwardly projecting cone-shaped rolling cutters which are rotatably mounted on journals carried by the body of the bit. The cutters have teeth or rock-crushing inserts on their conical surfaces, and are oriented by the journals to roll upon the bottom surface of the hole being drilled as the bit is rotated by the well string to which it is attached. A fluid, such as air, may be forced down the well string and discharged through the bit to flush cuttings upwardly in the well bore. The conical cutters commonly are mounted to the journals by means of both roller bearings and ball bearings, the roller bearings being subject to the radial forces imposed on the cutter during a drilling operation. In such operations, pulverized drill cuttings of rock or the like may find their way into the interior roller and ball bearings and cause undue bearing wear. Various methods have been suggested for preventing, or at least reducing, premature bearing wear; such methods include the use of seals to prevent pulverized rock cuttings from entering the bearing areas, or the use of lubricants, or compressed air flowing through an oblique channel to the bearings for lubricating and cooling the bearings and for sweeping pulverized rock away from the bearings. Representative of such bits are those described in U.S. Pat. Nos. 2,075,997; 2,076,002; 2,814,465; and 3,656,764.
The forces acting on such conical cutters during a drilling operation have both axial and radial components. Of these, the axial component was transmitted to the journal by means of the ball bearings, or by means of relatively small confronting frictional bearing surfaces interiorly of the bit, whereas the radial component was transmitted through the roller bearings. The heat generated at the bearing surfaces contributes materially to rapid bearing wear and premature failure.